The 49ers’ sturdy defense relies on a basic principle: Do not allow the big play.

Defensive coordinator Vic Fangio generally prefers pressure on the quarterback to come from a four-man pass rush, rather than leave the team vulnerable in coverage with exotic blitz packages.

The 49ers’ ability to supply heat with a four-man rush of Aldon Smith, Justin Smith, Ray McDonald and Ahmad Brooks has meshed well with a secondary that has been good about not allowing receivers to get over the top for long scoring plays.

So when the 49ers knew they would likely lose veteran strong safety Donte Whitner to his hometown Cleveland Brows in free agency, they focused their attention on a replacement who had the qualities they value from the position.

“He’s not an elite safety anymore, but he’s everything (the 49ers) were looking for,” an NFL scout told CSNBayArea.com. “He’s smart, hard-working and steady. He's not going to make big plays, but he won't give them up, either.”

Bethea is viewed as a “good locker-room guy” and great in the community. With free safety Eric Reid entering his second NFL season and the possibility cornerbacks Tramaine Brock and Chris Culliver could be enter a season as starters for the first time in their careers, leadership in the secondary was an essential quality for the 49ers.

Bethea also is durable. He has made 105 consecutive starts, including nine postseason games, dating back to a playoff game after the 2007 regular season.

Also, Bethea (5 foot 11, 206 pounds) was not called for a penalty the entire 2013 season, including the playoffs. Whitner (5-10, 208) was flagged for eight penalties, including five times for unnecessary roughness. It should be noted, however, that Whitner did not see any money deducted from his paychecks due to fines for illegal hits.

Bethea was twice named to the AFC Pro Bowl team (following the 2007 and ’09 seasons). He experienced a midseason slump last season after a down 2012. But he came on strong and had his best game in an AFC wild-card victory over the Kansas City Chiefs with nine tackles and a pass broken up.

According to Pro Football Focus, Whitner ranked as the sixth-best safety in the NFL last season, while Bethea was No. 53. Both players were on the field for more than 1,000 defensive snaps. Bethea and Whitner missed seven tackles apiece, but Bethea had 85 tackles compared to Whitner’s 59.

Whitner ranked better in pass coverage, according to PFF. He was targeted 48 times. He allowed 25 catches for 286 yards with two touchdowns and two interceptions. Bethea was targeted 33 times, and he surrendered 22 catches for 320 yards with three touchdowns and two interceptions.

Bethea, who turns 30 in July, is one year older than Whitner. And while the official contracts have not been turned into the league office, the 49ers are believed to have paid at least $1 million less per year than the Browns for their leader in the defensive backfield.